Corneal infection with herpes simplex virus-1 (HSV-1) causes herpetic stromal keratitis (HSK), a leading cause of infection-induced corneal blindness worldwide. Despite intensive research and substantial progress in understanding the pathogenesis of HSK, the management of this condition continues to be challenging. One significant hurdle is our poor understanding of the role of neuropeptides, secreted by abundant corneal nerve fibers, in the development of HSK lesions. Lack of such knowledge is an important problem because neuropeptides are well known to regulate both inflammation and tissue repair. The objective of this application is to determine what regulates substance P (SP) neuropeptide levels in the cornea after ocular HSV-1 infection, and how SP interactions with its receptor NK1R control the viral load and affects the development of HSK lesions. We will approach these questions in a mouse model by using SP-/- and NK1R-/- mice. We recently reported that blocking SP-NK1R interactions in the absence of replicating virus (clinical period) significantly reduced the development of HSK lesions. However, lack of SP-NK1R interactions during active viral replication in the cornea (pre-clinical period), enhances the severity of HSK lesions, as noted in SP- /- and NK1R-/- mice. Our preliminary results showed delayed viral clearance and reduced levels of epidermal growth factor (EGF), a corneal wound healing factor, in NK1R-/- mice. On the basis of our preliminary results, we hypothesize that SP, produced in HSV-1 infected corneas by macrophages and corneal nerves, promotes corneal tissue repair and regulates the influx, survival, and function of innate immune cells involved in viral clearance therefore, enhancing SP-mediated effects during active viral replication should reduce the development of severe HSK lesions. Three aims are proposed to address our hypothesis. In aim 1, experiments will be carried out to determine the role of corneal macrophages and sensory neurons in regulating the levels of SP peptide in HSV-1 infected corneas during the pre-clinical and clinical periods of HSK, respectively. In aim 2, experiments will be carried out t determine whether SP-NK1R interactions regulate viral load in the cornea by promoting the migration, survival, and functions of dendritic cells (DCs), inflammatory monocytes (IM) and natural killer (NK) cells in HSV-1 infected cornea. In aim 3, we will determine whether enhancing SP-mediated effects during the active viral replication period through topical application of EGF alone, or in combination with subconjunctival administration of SP, modulates the development of severe HSK lesions. The information generated by this study could aid in the development of novel pharmaceutical strategies to reduce HSV-1 induced chronic inflammation by promoting viral clearance and corneal tissue repair.